L-aspartyl-D-alanine-N-alkyl amides, such as disclosed in U.S. Pat. No. 4,411,925, are known to be useful as artificial sweeteners: ##STR1## In the series of compounds described by the above structure, the most potent material reported was the L-aspartyl-D-alanine amide of (+/-) t-butyl-cyclopropyl methylamine (R.sub.1 =R.sub.2 =R.sub.3 =CH.sub.3, n=0; wherein the sweetness potency (SP) was reported to be 1200 times sucrose.) It was furthermore emphasized that the nature of R in the above structure was important for sweetness potency, with R=CH.sub.3 (D-alanine) being especially preferred. In the typical case of the L-aspartyl-D-alanine amides having the structure, ##STR2## the sweetness potency decreases as R is increased, that is, for R=methyl, SP=1200, for R=ethyl, SP=500, and for R=isopropyl, SP=110.
Zeng et al., J. Agric. Food Chem. 39, 782-85 (1991), disclose L-aspartyl-D-alanine-N-phenyl amides wherein the benzene ring may have methyl-substituents: ##STR3## These compounds may be described as aniline amides of L-aspartyl-D-alanine. The individual members of this family of aniline amides were disclosed to have a sweetness potency that was at most 75 times that of sucrose except for the highly substituted 2,6-dimethylaniline amide which was disclosed to have a sweetness potency 500 times the sweetness of sucrose. In addition to the relatively low sweetness potency of most of the individual members of this aniline-based series of compounds, these compounds have a potential for toxicity that is known for aniline derivatives.
In addition, Ariyoshi, Bull. Chem. Soc. Japan, 57, 3197 (1984), discloses a series of L-aspartyl-D-alanyl-.alpha.-amino acid esters and L-aspartyl-D-valinyl-.alpha.-amino acid esters that are tasteless, bitter or of sweetness potency less than 50 times sucrose.